Serositis is a rare manifestation of chronic GvHD (cGvHD). No risk factors or laboratory changes associated with this syndrome have been recognized to date, and outcomes have not been described in a large series. We searched our institutional database for patients undergoing allogeneic hematopoietic cell transplant identified as having serositis or pericarditis. Laboratory studies from prior to diagnosis, at diagnosis and post diagnosis of serositis, as well as outcomes from invasive procedures were included. Twenty patients met criteria for cGvHD-associated serositis, and all but three patients had a prior diagnosis of cGvHD. Fifteen were male, and the complication occurred in the setting of immunosuppressant taper in 12 cases. Ten patients required invasive interventions, including pericardial window or stripping. A significant increase in blood monocytes and decrease in serum albumin were identified at diagnosis compared with pre-diagnosis. Out of 20 patients, 17 were treated with steroids, with 12 demonstrating a complete response. These data suggest that cGvHD-associated serositis occurs mainly in the setting of treated as opposed to de novo cGvHD and biomarkers associated with the syndrome include a decrease in albumin and an increase in absolute monocyte count. Outcome data from larger series are required to better understand the optimal management of this rare complication.